Image projection apparatus

ABSTRACT

Provided is an image projection apparatus, such as a projector, including a light source; an image generating element such as a DMD that receives light from the light source and forms an image; an image generating unit that irradiates the image generating element with the light from the light source; a first optical system including multiple transmission refractive optical elements; a second optical system arranged on an optical path of outgoing light of the first optical system and including a reflection optical element; and a projection optical system that enlarges and projects an image conjugate to the image generated by the image generating element as a projected image. The light source, the image generating unit, and the first optical system are arranged side by side in series in a direction parallel with the projected image plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/611,508 filed Sep. 12, 2012, which claims priority Japanese PatentApplication No. 2011-203430 filed Sep. 16, 2011, the entire contents ofeach of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image projection apparatus such as aprojector.

2. Description of the Related Art

Heretofore, there has been known an image projection apparatus includinga DMD (Digital Mirror Device) serving as an image generating elementthat generates an image based on image data supplied from a personalcomputer or the like; an lighting unit that irradiates the imagegenerating element with light from a light source; and a projectionoptical system for forming an optical image, which is generated by theimage generating element and the lighting unit, on a projection plane(for example, Japanese Patent Application Laid-open No. 2008-134432).

Specifically, the light from the light source which travels in parallelwith an image generation surface of the DMD is reflected toward theimage generation surface of the DMD by an illumination optical system,such as a reflection mirror, and is applied onto the image generationsurface of the DMD. On the imaging generation surface of the DMD, aplurality of movable micromirrors is arranged in a lattice. Eachmicromirror allows the mirror surface thereof to be inclined about atorsion axis by a predetermined angle, and allows the mirror surface tohave two states of “ON” and “OFF”. When the micromirror is in the “ON”state, the micromirror reflects light from the light source toward theprojection optical system. When the micromirror is in the “OFF” state,the mirror reflects the light from the light source toward a lightabsorber provided in the apparatus. Accordingly, individually drivingthe mirrors makes it possible to control the projection of light foreach pixel of image data and to generate an optical image. The opticalimage generated by the DMD passes through the projection optical systemand is formed on the projection plane.

Additionally, Japanese Patent Application Laid-open No. 2008-250277discloses an image projection apparatus including a projection opticalsystem composed of a first optical system formed of a plurality oflenses and a second optical system including a concave mirror. In theimage projection apparatus disclosed in Japanese Patent ApplicationLaid-open No. 2008-250277, the first optical system forms anintermediate optical image conjugate to the optical image generated bythe image generating element between the first optical system and thesecond optical system, and the second optical system enlarges andprojects an image conjugate to the intermediate optical image theintermediate optical image on the projection plane. The configuration ofthe projection optical system as described above achieves point-blankprojection.

FIG. 17 is a diagram illustrating a usage example of the imageprojection apparatus disclosed in Japanese Patent Application Laid-openNo. 2008-250277.

As illustrated in FIG. 17, in the image projection apparatus disclosedin Japanese Patent Application Laid-open No. 2008-250277, the opticalimage generated by an image generating element 12 advances in adirection orthogonal to a projection plane (screen) 101, passes througha first optical system 70, and is reflected by a concave mirror 42serving as the second optical system and projected on the projectionplane.

As illustrated in FIG. 17, the image projection apparatus is generallyused in the state of being placed on a desk 100 or the like which isopposed to the projection plane 101. The desk, chair, and the like usedby a user are also arranged to be opposed to the projection plane 101.As disclosed in Japanese Patent Application Laid-open No. 2008-250277,an image projection apparatus 1A in which the image generating element12, an illumination unit 20, and the first optical system 70 arearranged side by side in series in the direction orthogonal to the planeof a projected image projected on the projection plane 101 is elongatedin the direction (X-direction in the figure) orthogonal to the projectedimage plane. Thus, when the image projection apparatus 1A is elongatedin the direction orthogonal to the projected image plane, aninstallation space for the image projection apparatus 1A is required inthe direction orthogonal to the projection plane 101. As a result, in anarrow indoor space, a sufficient space cannot be secured in thedirection orthogonal to the projection plane 101, and the layout spacefor the desk and chair used by the user is limited. This results in aproblem of impairing the convenience. Note that the phrase “arrangedside by side in series” described above and below refers to anarrangement in which, on an optical path of outgoing light of an opticalsystem formed of a certain optical element or a plurality of opticalelements, the incidence plane of another optical system formed ofanother optical element or a plurality of optical elements is arranged.

In the above description, the case where the image projection apparatusis used by being placed on the desk 100 or the like has been described.However, even in the case where the image projection apparatus is usedby being hung from the ceiling or the like, when the image projectionapparatus is elongated in the direction orthogonal to the projectionplane 101, the convenience is impaired for the following reason. Thatis, in the case of installing the image projection apparatus on theceiling, the image projection apparatus may interfere with lightingequipment or the like arranged on the ceiling, so that the installationspace for the image projection apparatus is limited and the convenienceis impaired.

The present invention has been made in view of the above-mentionedproblem, and it is an object of the present invention to provide animage projection apparatus capable of shortening the length in thedirection orthogonal to the projection plane of the apparatus, ascompared with the related art.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

An image projection apparatus comprising: a light source; an imagegenerating unit that generates an image by using the light source; and aprojection optical unit that projects the image generated by the imagegenerating unit.

The image generating unit and the projection optical unit are arrangedin a vertical direction, the light source is arranged beside the imagegenerating unit, and the projection optical unit projects the image on aplane positioned in a direction orthogonal to the vertical direction.

The above-mentioned image generating unit corresponds to theafter-mentioned illumination unit 20 that reflects light from a lightsource 61 and irradiates a DMD 12 with the light to generate an opticalimage.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an optical path from a projector to aprojection plane of this embodiment;

FIG. 2 is a schematic perspective view illustrating the configuration ofthe projector;

FIG. 3 is an appearance perspective view illustrating a relevant portionof the projector;

FIG. 4 is a perspective view of an image generating unit;

FIG. 5 is a schematic perspective view of a light source unit;

FIG. 6 is a perspective view illustrating a bottom surface of aprojector 1;

FIG. 7 is a perspective view illustrating a state where a light sourcereplacement cap from an apparatus;

FIG. 8 is a schematic perspective view illustrating optical componentsarranged in an illumination unit;

FIG. 9 is a perspective view illustrating the illumination unit, theimage generating unit, and a projection lens unit of a first opticalsystem unit;

FIG. 10 is a perspective view illustrating the first optical systemunit, as well as the illumination unit and the image generating unit;

FIG. 11 is a sectional view taken along the line A-A of FIG. 10;

FIG. 12 is a perspective view illustrating a second optical system unit,as well as the first optical system unit, the illumination unit, and theimage generating unit;

FIG. 13 is a perspective view illustrating a second optical system heldby the second optical system unit, as well as the projection lens unit,the illumination unit, and the image generating unit;

FIG. 14 is a perspective view illustrating an optical path from thefirst optical system to the projection plane;

FIG. 15 is a schematic diagram illustrating the arrangement relationshipamong the units within the apparatus;

FIG. 16 is a diagram illustrating a usage example of the projector ofthis embodiment;

FIG. 17 is a diagram illustrating a usage example of a related artprojector;

FIG. 18 is a diagram illustrating a usage example of a projector inwhich a light source and an illumination unit are arranged in adirection orthogonal to the projection plane;

FIG. 19 is a diagram illustrating a modified example of the projector ofthis embodiment; and

FIG. 20 is a diagram illustrating another usage example of the projectorof this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of a projector will be described as an imageprojection apparatus to which the present invention is applied. FIG. 1is a diagram illustrating an optical path from a projector 1 to aprojection plane 101 according to this embodiment. FIG. 2 is a schematicperspective view illustrating the configuration of the projector 1. FIG.3 is an appearance perspective view illustrating a relevant portion ofthe projector 1. Note that in the following description, assume that thenormal direction of the projection plane 101 is defined as anX-direction; the short-axis direction (vertical direction) of theprojection plane is defined as a Y-direction; and the long-axisdirection (horizontal direction) of the projection plane 101 is definedas a Z-direction.

As illustrated in FIGS. 1 to 3, the projector 1 includes an imagegenerating unit 10, which includes a DMD 12 (Digital Mirror Device)serving as an image generating element; a light source unit 60 includinga light source 61; an illumination unit 20 that reflects light from thelight source 61 and irradiates the DMD 12 with the light to generate anoptical image; and a projection optical system for projecting the imageon the projection plane 101. The projection optical system includes afirst optical system unit 30 serving as a coaxial system including atleast one refractive optical system and having positive power, and asecond optical system unit 40 including at least one reflecting surfacehaving positive power.

FIG. 4 is a perspective view of the image generating unit 10.

As illustrated in the figure, the image generating unit 10 includes aDMD board 11 mounted with the DMD 12. The DMD 12 is mounted on a socket11 a which is provided on the DMD board 11 with the image generationsurface, on which the micromirrors are arranged in a lattice, facingupward. The DMD board 11 is provided with a drive circuit for drivingthe DMD mirrors, for example. A section in which the DMD 12 of the DMDboard 11 is mounted is penetrated, and a heat sink 13 serving as coolingmeans for cooling the DMD 12 contacts the back surface (surface oppositeto the image generation surface) of the DMD 12 through a through-holewhich is not illustrated. The heat sink 13 is pressurized by a clampingplate 14 against the surface opposite to the surface on which the socket11 a of the DMD board 11 is provided. The clamping plate 14 is fixed tothe DMD board 11 at four sections by screws 15, thereby allowing theheat sink 13 to be fixed to the DMD board 11.

FIG. 5 is a schematic perspective view of the light source unit 60.

The light source unit 60 includes a light source bracket 62 which ismounted with the light source 61 such as a halogen lamp, a metal halidelamp, or a high-pressure mercury lamp. This light source bracket 62 isprovided with a connector unit 62 a to be connected to apower-supply-side connector which is not illustrated and which isconnected to a power supply unit 80 (see FIG. 15).

The light source unit 60 also includes a holder 64 that holds areflector, which is not illustrated, and the like. The holder 64 isscrewed into the light source bracket 62. The holder 64 is provided withthree light source positioning units 64 a 1 to 64 a 3 for positioning onan illumination bracket 26 of the illumination unit 20 to be describedlater. The light source positioning unit 64 a 3 provided on the topsurface of the holder 64 has a protrusion shape, and the two lightsource positioning units 64 a 1 and 64 a 2 provided on the side of thelight source bracket 62 of the holder 64 have a hole shape. Theillumination bracket 26 of the illumination unit 20 includes a lightsource positioned unit 26 a 3 which has a hole shape and which is fittedwith the light source positioning unit 64 a 3 which has a protrusionshape and which is provided on the top surface of the holder 64; and twolight source positioned units 26 a 1 and 26 a 2 which have a protrusionshape and which are fitted with the two light source positioning units64 a 1 and 64 a 2 which have a hole shape and which are provided on theside of the light source bracket 62 of the holder 64 (see FIG. 9). Thethree light source positioning units 64 a 1 to 64 a 3 of the holder 64are fitted into the three light source positioned units 26 a 1 to 26 a 3which are provided on the illumination bracket 26 of the illuminationunit 20, thereby allowing the light source unit 60 to be positioned andfixed onto the illumination unit 20. The light source unit 60 isconfigured to be detachable from the back surface of the apparatus body.

FIG. 6 is a perspective view illustrating a bottom surface 53 of theprojector 1. FIG. 7 is a perspective view illustrating a state where alight source replacement cap 54 is dismounted from the apparatus.

As illustrated in FIG. 6, the light source replacement cap 54 isprovided on the bottom surface of the projector 1, and the light sourcereplacement cap 54 is provided with a rotary lever 54 a. When the rotarylever 54 a is rotated, the fixation between the light source replacementcap 54 and the apparatus body is released to thereby allow the lightsource replacement cap 54 to be removed from the apparatus body. Whenthe light source replacement cap 54 is removed, the surface opposite tothe surface where the light source 61 of the light source bracket 62 ofthe light source unit 60 is mounted is exposed. The light source bracket62 is mounted with a handle unit 65 so as to be rotatable with respectto the light source bracket 62.

In the case of dismounting the light source unit 60 from the apparatusbody, the handle unit 65 is rotated and gripped so as to be drawn to thefront side in the figure, thereby dismounting the light source unit 60from the apparatus body. When a brand-new light source unit 60 ismounted on the apparatus body, the connector unit 62 a is connected tothe power-supply-side connector, which is not illustrated, of theapparatus body, and the three light source positioning units 64 a 1 to64 a 3 of the holder 64 are fitted into the light source positionedunits 26 a 1-26 a 3 provided on the illumination bracket 26 of theillumination unit 20, thereby positioning the light source unit 60 ontothe apparatus body. Then, the light source replacement cap 54 is mountedon the bottom surface. The light source replacement cap 54 is providedwith a pressing unit (not illustrated) for pressing the light sourceunit 60 into the apparatus body. If the light source unit 60 is notproperly mounted on the apparatus body, the light source unit 60 ispressed in by the pressing unit upon mounting of the light sourcereplacement cap 54 on the bottom surface, thereby properly mounting thelight source unit 60 on the apparatus body. Then, the rotary lever 54 ais rotated to fix the light source replacement cap 54 to the bottomsurface.

The bottom surface 53 is provided with three leg portions 55. Therotation of the leg portions 55 enables change of the amount ofprojection from the bottom surface and adjustment in the heightdirection (Y-direction).

Next, the illumination unit 20 will be described.

FIG. 8 is a schematic perspective view illustrating optical componentsarranged in the illumination unit 20. FIG. 9 is a perspective viewillustrating the illumination unit 20, the image generating unit 10, aprojection lens unit 31 of the first optical system unit 30.

The illumination unit 20 includes a color wheel 21, a light tunnel 22,two relay lenses 23, a cylinder mirror 24, and a concave mirror 25.These components are held by the illumination bracket 26. As illustratedin FIG. 9, the illumination bracket 26 also includes an OFF opticalplate 27 which is irradiated with light when the micromirrors of the DMD12 are in the “OFF” state.

As illustrated in FIG. 2, an irradiation through-hole 26 d for exposingthe DMD 12 is provided in the lower surface of the illumination bracket26. The image generating unit 10 is positioned and fixed onto theillumination bracket 26 by screws.

As illustrated in FIG. 9, through-holes 26 c 1 to 26 c 4 through whichscrews for screwing the first optical system unit 30 are provided in thevicinity of four corners of a top surface 26 b of the illuminationbracket 26 (FIG. 9 illustrates 26 c 1 and 26 c 2). Additionally,positioning holes 26 e 1 and 26 e 2 for positioning the first opticalsystem unit 30 on the illumination unit 20 are provided adjacent to thethrough-holes 26 c 1 and 26 c 2 on the side where the OFF optical plate27 is arranged. A notch is formed between the through-holes 26 c 1 and26 c 2 of the top surface 26 b of the illumination bracket 26 so as toprevent interference with the second optical system unit 40 to bescrewed into the first optical system unit 30. The positioning hole 26 e1 formed on the side where the color wheel 21 is arranged is a mainreference for positioning and has a round hole shape. The positioninghole 26 e 2 formed on the side opposite to the side where the colorwheel 21 is arranged is a sub reference for positioning and is a longhole extending in the Z-direction. In the vicinity of the through-holes26 c 1 to 26 c 4, there are positioning protrusions 26 f which projectfrom the top surface 26 b of the illumination bracket 26 and are usedfor positioning the first optical system unit 30 in the Y-direction. Inthe case of increasing the positioning accuracy in the Y-directionwithout providing the positioning protrusions 26 f, it is necessary toincrease the flatness of the entire top surface of the illuminationbracket 26, which leads to an increase in cost. On the other hand, whenthe positioning protrusions 26 f are provided, it is only necessary toincrease the flatness of the portion of the positioning protrusions 26f. This makes it possible to suppress an increase in cost and toincrease the positioning accuracy in the Y-direction.

The illumination unit 20 also includes an illumination cover 28 thatcovers the optical system components such as the color wheel 21 and thelight tunnel 22.

The color wheel 21 has a disc shape and is fixed to a motor shaft of acolor motor 21 a. The color wheel 21 is provided with filters of R(red), G (green), B (blue), or the like in a rotational direction. Thelight focused by a reflector which is not illustrated and which isprovided on the holder 64 of the light source unit 60 passes through anexit window 63 and reaches a peripheral edge of the color wheel 21. Thelight is separated into R, G, and B light beams by time division throughthe rotation of the color wheel 21.

The light beams separated by the color wheel 21 enter the light tunnel22. The light tunnel 22 has a square cylinder shape, and the innerperipheral surface thereof is a mirror surface. The light beams enteringthe light tunnel 22 are reflected a plurality of times on the innerperipheral surface of the light tunnel 22, are made into a uniformsurface light source, and exit toward the relay lenses 23.

The light having passed through the light tunnel 22 is transmittedthrough the two relay lenses 23, is reflected by the cylinder mirror 24and the concave mirror 25, and is focused on the image generationsurface of the DMD 12.

A plurality of movable micromirrors is arranged in a lattice on theimage generation surface of the DMD 12. Each micromirror allows themirror surface thereof to be inclined about a torsion axis by apredetermined angle, and allows the mirror surface to have two states of“ON” and “OFF”. In the “ON” state, the micromirror reflects the lightfrom the light source 61 toward the first optical system 70 (see FIG.1). In the “OFF” state, the micromirror reflects the light from thelight source 61 toward the OFF optical plate 27 (see FIG. 9) provided onthe illumination unit 20. Accordingly, individually driving the mirrorsenables control of the projection of light for each pixel of image dataand generation of an optical image.

The light reflected toward the OFF optical plate 27 is converted intoheat to be absorbed and cooled by a flow of outside air.

FIG. 10 is a perspective view illustrating the first optical system unit30, the illumination unit 20, and the image generating unit 10.

As illustrated in FIG. 10, the first optical system unit 30 includes theprojection lens unit 31 that holds the first optical system 70 (seeFIG. 1) formed of a plurality of lenses, and a lens holder 32 that holdsthe projection lens unit 31. The lens holder 32 is provided with fourleg portions 32 a 1 to 32 a 4, and the leg portions 32 a 1 to 32 a 4have screw holes for allowing the leg portions to be screwed into theillumination bracket 26.

FIG. 11 is a sectional view taken along the line A-A of FIG. 10.

As illustrated in FIG. 11, the leg portions 32 a 1 and 32 a 2 (see FIG.3) on the side of the OFF optical plate 27 are provided with positionedprotrusions 32 b 1 and 32 b 2, respectively. The positioned protrusion32 b 1 on the right side of the figure is inserted into the positioninghole 26 e 1 which has a round hole shape provided in the top surface 26b of the illumination bracket 26 and serves as the main reference forpositioning. The positioned protrusion 32 b 2 on the left side of thefigure is inserted into the positioning hole 26 e 2 which serves as thesub reference for positioning and which has a long hole shape. Thus, thepositioning in each of the Z-axis direction and the X-axis direction isachieved. When screws 37 are inserted into the through-holes 26 c 1 to26 c 4, which are formed in the top surface 26 b of the illuminationbracket 26, and the screws 37 are screwed into the screw holes formed inthe lens holder 32, thereby positioning and fixing the first opticalsystem unit 30 onto the illumination unit 20.

As illustrated in FIG. 10 described above, the projection lens unit 31is provided with a focus gear 36, and the focus gear 36 engages with anidler gear 35. The idler gear 35 engages with a lever gear 34. A focuslever 33 is fixed to the rotating shaft of the lever gear 34. A leadingend of the focus lever 33 is exposed from the apparatus body asillustrated in FIG. 6 described above.

When the focus lever 33 is moved, the focus gear 36 rotates through thelever gear 34 and the idler gear 35. When the focus gear 36 is rotated,the plurality of lenses forming the first optical system 70 within theprojection lens unit 31 moves in a predetermined direction to therebyadjust the focus of the projected image.

As illustrated in FIGS. 10 and 11, the first optical system unit 30 hasfour screw through-holes 32 c 1 to 32 c 4 through which screws 48 forscrewing the second optical system unit 40 into the first optical systemunit 30 (FIG. 10 illustrates three screw through-holes and illustrates astate where the screws 48 are penetrated through the screw through-holes32 c 1 to 32 c 4). In the vicinity of the screw through-holes 32 c 1 to32 c 4, second optical system unit positioning protrusions 32 d 1 to 32d 4 projecting from the surface of the lens holder 32 are formed (FIG.10 illustrates 32 d 1 to 32 d 3).

FIG. 12 is a perspective view illustrating the second optical systemunit 40, as well as the first optical system unit 30, the illuminationunit 20, and the image generating unit 10. FIG. 13 is a perspective viewillustrating a second optical system held by the second optical systemunit 40, as well as the projection lens unit 31, the illumination unit20, and the image generating unit 10.

The second optical system unit 40 holds a reflection mirror 41constituting the second optical system, and a concave mirror 42 having aconcave shape. The second optical system unit 40 also holds atransmitting glass 51 which allows the optical image reflected on theconcave mirror 42 to be transmitted and which is used for dust proofingof the optical system components within the apparatus. The reflectionmirror 41 and the transmitting glass 51 are held by a mirror bracket 43,and the concave mirror 42 is held by a free mirror bracket 44. Themirror bracket 43 and the free mirror bracket 44 are held by a mirrorholder 45.

The reflection mirror 41 is positioned and fixed to the mirror bracket43 in such a manner that both ends in the Z-direction of the reflectionmirror 41 are pressed against the mirror bracket 43 by mirror pressingmembers 46 having a plate spring shape. One end in the Z-direction ofthe reflection mirror 41 is fixed by two mirror pressing members 46, andthe other end thereof is fixed by one mirror pressing member 46.

The transmitting glass 51 is also positioned and fixed onto the mirrorbracket 43 in such a manner that both ends in the Z-direction of thetransmitting glass 51 are pressed against the mirror bracket 43 by glasspressing members 47 having a plate spring shape. Each of the both endsin the Z-direction of the transmitting glass 51 is fixed by one glasspressing member 47.

A substantially central portion of the concave mirror 42 at an end onthe side of the transmitting glass 51 is pressed against the free mirrorbracket 44 by a free mirror pressing member 49 having a plate springshape, and the first optical system side is fixed to the free mirrorbracket 44 by screws.

Cylindrical screw stops 45 a 1 to 45 a 4 for screwing the first opticalsystem unit 30 are formed on the lower surface of the mirror holder 45(as for the screw stops 45 a 1 and 45 a 2, see FIG. 12; as for the screwstop 45 a 3, see FIG. 2). The second optical system unit 40 allows thescrews 48 to be penetrated through the screw through-holes 32 c 1 to 32c 4 formed in the lens holder 32 of the first optical system unit 30.The screws 48 are screwed into the screw stops 45 a 1 to 45 a 4, therebybeing screwed into the first optical system unit 30. At this time, thelower surface of the mirror holder 45 of the second optical system unit40 contacts the second optical system unit positioning protrusions 32 d1 to 32 d 4 of the lens holder 32, thereby positioning and fixing thesecond optical system unit 40 in the Y-direction.

FIG. 14 is a perspective view illustrating an optical path from thefirst optical system 70 to the projection plane 101 (screen).

The optical image transmitted through the projection lens unit 31forming the first optical system 70 forms an intermediate imageconjugate to the optical image generated by the DMD 12 between thereflection mirror 41 and the concave mirror 42. This intermediate imageis formed as a curved surface image between the reflection mirror 41 andthe concave mirror 42. Next, the optical image enters the concave mirror42 having a concave shape, and the intermediate image is made into “afurther enlarged image” by the concave mirror 42 and projected andfocused on the projection plane 101.

In this manner, the projection optical system is formed of the firstoptical system 70 and the second optical system, and the intermediateimage is formed between the first optical system 70 and the concavemirror 42 of the second optical system and is enlarged and projected bythe concave mirror 42, thereby enabling shortening of the projectiondistance and use even in a narrow conference room, for example.

The surface reflecting the light of the concave mirror 42 can be formedinto a spherical surface shape, a rotation symmetry aspherical surfaceshape, a free-form surface shape, or the like.

FIG. 15 is a schematic diagram illustrating the arrangement relationshipamong the units within the apparatus.

As illustrated in the figure, the image generating unit 10, theillumination unit 20, the first optical system unit 30, and the secondoptical system unit 40 are stacked and arranged in the Y-direction whichis the short-axis direction of the projection plane. The light sourceunit 60 is arranged in the Z-direction, which is the long-axis directionof the projection plane, with respect to the stacked body obtained bystacking the image generating unit 10, the illumination unit 20, thefirst optical system unit 30, and the second optical system unit 40.

In the arrangement of the units in this manner, the light emitted fromthe light source 61 travels in the Z-direction parallel with theprojection plane, is reflected by the cylinder mirror 24 and the concavemirror of the illumination unit 20 in the Y-direction parallel with theprojection plane, and enters the DMD 12.

As illustrated in FIG. 1, the optical image generated by the DMD 12travels in the Y-direction parallel with the projection plane, istransmitted through the first optical system 70 formed of a plurality ofoptical lenses, and enters the second reflection mirror 41. The lightincident on the second reflection mirror 41 is reflected in theZ-direction orthogonal to the projection plane. The light is thenreflected by the concave mirror 42 and is applied onto the projectionplane 101. Thus, the second optical system is formed of the reflectionmirror 41 and the concave mirror 42, thereby allowing the lighttransmitted through the first optical system 70 parallel with theprojection plane 101 to be projected toward the projection plane 101.

FIG. 16 is a diagram illustrating a usage example of the projector 1 ofthis embodiment. FIG. 17 is a diagram illustrating a usage example ofthe related art projector 1A. FIG. 18 is a diagram illustrating a usageexample of a projector 1B in which the light source 61 and theillumination unit 20 are arranged side by side in the directionorthogonal to the projection plane 101.

As illustrated in FIGS. 16 to 18, in the case of using the projector 1in a conference room, for example, the projector 1 is placed on thetable 100 and an image is projected on the projection plane 101 such asa white board.

As illustrated in FIG. 17, in the related art projector 1A, the DMD 12(image generating element), the illumination unit 20, and the firstoptical system 70 are arranged side by side in series in the directionorthogonal to the projected image plane, so that the projector 1A iselongated in the direction (X-direction) orthogonal to the projectionplane of the projector 1A and occupies a large space in the directionorthogonal to the projection plane 101. A chair to be used by a personwho observes the image projected on the projection plane 101, or a deskto be used is generally arranged in the direction orthogonal to theprojection plane. Accordingly, if the projector occupies a large spacein the direction orthogonal to the projection plane, the layout spacefor the chair or desk is limited, resulting in deteriorating theconvenience.

The projector 1B illustrated in FIG. 18 has a configuration in which theDMD 12 (image generating element), the illumination unit 20, and thefirst optical system 70 are arranged in series in a direction parallelwith the projected image plane. Accordingly, as compared with theprojector 1B illustrated in FIG. 17, the length in the directionorthogonal to the projection plane 101 can be reduced. However, in theprojector 1B illustrated in FIG. 18, the outgoing plane of the lightsource 61 is arranged in the direction orthogonal to the projected imageplane with respect to the illumination unit 20. This makes it difficultto sufficiently reduce the length in the direction orthogonal to theprojection plane 101 of the projector.

On the other hand, in this embodiment, the light source unit 60, theimage generating unit 10, the illumination unit 20, the first opticalsystem unit 30, and the reflection mirror 41 are arranged in series in adirection parallel with the projected image plane. Note that the phrase“in series in the direction parallel with the projected image plane”herein described is not limited to the configuration in which the unitsare arranged side by side linearly. The phrase “in series in thedirection parallel with the projected image plane” herein describedrefers to a configuration in which units are arranged side by side inseries in one of the Y-direction and the Z-direction which aredirections parallel with the projected image plane with respect to theadjacent unit. Accordingly, also the configuration in which the imagegenerating unit 10, the illumination unit 20, the first optical systemunit 30, and the reflection mirror 41 of this embodiment are arranged inseries in the Y-direction which is a direction parallel with theprojected image plane and the light source unit 60 and the illuminationunit 20 are arranged in series in the Z-direction which is a directionparallel with the projected image plane corresponds to the configurationin which the units are arranged “in series in the direction parallelwith the projected image plane”. In this manner, the light source unit60, the image generating unit 10, the illumination unit 20, the firstoptical system unit 30, and the reflection mirror 41 are arranged sideby side in series in the direction parallel with the projected imageplane, thereby making it possible to reduce the length of the projector1 in the direction (X-direction) orthogonal to the projection plane 101as illustrated in FIG. 16. This prevents the projector 1 frominterfering with the installation space for a chair or desk, and makesit possible to provide the projector 1 with high convenience.

Further, in this embodiment, as illustrated FIG. 15 described above, thepower supply units 80 for supplying power to the light source 61 and theDMD 12 are stacked and arranged above the light source unit 60. Thus, itis also possible to reduce the length in the Z-direction of theprojector 1.

Further, in this embodiment, the light source 61 is arranged so as toirradiate light in the Z-direction, but the light source 61 may bearranged so as to irradiate light in the Y-direction as illustrated inFIG. 19. In this case, the light from the light source 61, which exitsin the Y-direction, is reflected in the Z-direction by the reflectionmirror 41. The subsequent optical path is the same as described above.Also in this configuration, the optical path from the light source 61 tothe reflection mirror 41 is in parallel with the projection plane 101,and the light source unit 60 prevents an increase in the length of theprojector 1 in the direction (X-direction) orthogonal to the projectionplane 101 due to the arrangement in which the image generating unit 10,the illumination unit 20, the first optical system unit 30, and thesecond optical system unit 40 are arranged in series in the directionparallel with the projection plane.

FIG. 20 is an explanatory diagram illustrating another usage example ofthe projector of this embodiment.

As illustrated in FIG. 20, the projector 1 of this embodiment can alsobe used by being hung from a ceiling 105. Also in this case, theprojector 1 of this embodiment has a short length in the directionorthogonal to the projection plane 101, which allows the projector 1 tobe installed without interfering with a lighting equipment 106 arrangedon the ceiling 105 upon installation of the projector 1 on the ceiling105.

Further, in this embodiment, the second optical system is formed of thereflection mirror 41 and the concave mirror 42. Alternatively, thesecond optical system may be formed only of the concave mirror 42. Thereflection mirror 41 may be a plane mirror, a mirror having a positiverefractive power, or a mirror having a negative refractive power.Further, in this embodiment, a concave mirror is used as the concavemirror 42, but a convex mirror can also be used. In this case, the firstoptical system 70 is formed so as not to form an intermediate imagebetween the first optical system 70 and the concave mirror 42.

The above-mentioned embodiment is illustrated by way of example, and thepresent invention has specific advantageous effects for the followingmodes (1) to (3).

(1) An image projection apparatus, such as the projector 1, including:the light source 61; an image generating element, such as the DMD 12,which receives light from the light source and generates an image; theillumination unit 20 which irradiates the image generating element withthe light from the light source 61; a first optical system 70 includinga plurality of transmission refractive optical elements; a secondoptical system which is arranged on an optical path of light emittedfrom the first optical system and includes a reflection optical element;and a projection optical system that enlarges and projects an imageconjugate to the image generated by the image generating element as aprojected image, in which the light source 61, the illumination unit 20,and the first optical system 70 are arranged side by side in a directionparallel with the plane of the projected image.

The configuration as described above allows the apparatus to beshortened in the direction orthogonal to the projected image plane.Thus, the apparatus can be shortened in the direction orthogonal to theprojected image plane, thereby preventing the installation space for theapparatus from being required in the direction orthogonal to theprojected image plane. As a result, in the case of using the imageprojection apparatus by being placed on a desk or the like, theapparatus can be prevented from interfering with the layout of a desk ora chair even in a narrow indoor space. In the case of using the imageprojection apparatus by being hung from the ceiling or the like, theimage projection apparatus can be prevented from interfering withlighting equipment or the like arranged on the ceiling upon installationof the image projection apparatus, so that the image projectionapparatus can be installed at a predetermined position. Consequently, itis possible to provide an image projection apparatus with highconvenience.

(2) In the image projection apparatus according to the mode (1)described above, the light source unit 60 is configured to emit lightfrom the light source 61 in parallel with the image generation surfaceof the image generating element. This configuration eliminates the needto provide a reflection mirror or the like, unlike the configurationillustrate in FIG. 18, and reduces the number of components, which leadsto a reduction in cost of the apparatus. As illustrated in FIG. 15described above, the power supply unit 80 can be arranged in a spaceabove the light source unit 60.

(3) In the image projection apparatus according to the mode (1) or (2)described above, the projection optical system includes the firstoptical system unit 30 including a first optical system 70, and thesecond optical system unit 40 including a second optical system; and theimage generating element, light source unit 60 and the first opticalsystem unit 30 are positioned and fixed onto the illumination unit 20,and the second optical system unit 40 are positioned and fixed onto thefirst optical system unit 30.

With this configuration, as described in the above embodiment, theoptical path from the light source 61 to the first optical system 70 canbe configured to be in parallel with the projection plane 101.

According to the present invention, an image generating unit and aprojection optical unit are arranged in a vertical direction and a lightsource is arranged beside the image generating unit to project an imageon a plane positioned in a direction orthogonal to the verticaldirection, thereby shortening the length in the direction orthogonal tothe projected image plane of the apparatus, as compared with an imageprojection apparatus in which the image generating unit and theprojection optical unit are arranged side by side in series in thedirection orthogonal to the plane of a projected image projected on theprojection plane. Since the apparatus can be shortened in the directionorthogonal to the projected image plane, an installation space requiredfor the apparatus can be suppressed in the direction orthogonal to theprojected image plane. As a result, in the case of using the imageprojection apparatus by being placed on a desk or the like, theapparatus can be prevented from interfering with the layout of the deskor chair even in a narrow indoor space. Additionally, in the case ofusing the image projection apparatus by being hung from the ceiling orthe like, when the image projection apparatus is installed on theceiling, the image projection apparatus can be prevented frominterfering with lighting equipment or the like arranged on the ceiling.This makes it possible to install the image projection apparatus at apredetermined position. Consequently, it is possible to provide an imageprojection apparatus with high convenience.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. An image projection apparatus comprising aprojection optical system that projects an image, the projection opticalsystem comprises: a first optical system formed of a plurality oflenses; and a second optical system including a first mirror, a secondmirror, a transmitting glass, and a mirror holder, wherein the firstmirror is positioned on an optical path of light output from the firstoptical system, the second mirror is positioned on an optical path oflight reflected from the first mirror, the transmitting glass ispositioned on an optical path of light reflected from the second mirror,and wherein the mirror holder holds a first bracket which holds at leastthe first mirror and the transmitting glass.
 2. The image projectionapparatus according to claim 1, wherein the mirror holder holds a secondbracket which holds the second mirror.
 3. The image projection apparatusaccording to claim 2, wherein a portion of the second mirror at an endon the side of the transmitting glass is pressed against the secondbracket by a plate spring, and a first optical system side of the secondmirror is fixed to the second bracket by screws.
 4. The image projectionapparatus according to claim 2, wherein the first bracket is positionedon a side of a reflecting surface of the first mirror, and the secondbracket is positioned on a side of a reflecting surface of the secondmirror.
 5. The image projection apparatus according to claim 1, whereinthe projection optical system is housed in an apparatus body, and lightreflected from the second mirror outputs from an upper surface or a backsurface of the apparatus body.
 6. The image projection apparatusaccording to claim 1, further comprising a light source and anillumination unit that illuminates an image generating unit, wherein aplane formed by the light source, the illumination unit, and theprojection optical system corresponds to the plane positioned in adirection orthogonal to a vertical direction, and the light source, theillumination unit, and the projection optical system are arranged toface a plane on which the image generated by the image generating unitis projected.
 7. The image projection apparatus according to claim 1,wherein the second mirror is a concave mirror.
 8. An optical systemcomprising: a first optical system formed of a plurality of lenses; anda second optical system including a first mirror, a second mirror, atransmitting glass, and a mirror holder, wherein the first mirror ispositioned on an optical path of light output from the first opticalsystem, the second mirror is positioned on an optical path of lightreflected from the first mirror, the transmitting glass is positioned onan optical path of light reflected from the second mirror, and whereinthe mirror holder holds a first bracket which holds at least the firstmirror and the transmitting glass.
 9. The optical system according toclaim 8, wherein the mirror holder holds a second bracket which holdsthe second mirror.
 10. The optical system according to claim 9, whereina portion of the second mirror at an end on a side of the transmittingglass is pressed against the second bracket by a plate spring, and afirst optical system side of the second mirror is fixed to the secondbracket by screws.